A few days ago, MG Tia O’Neill (class of 2013) had a couple of questions about getting rid of tent caterpillar tents. These little pests were such…such…well, pests last year that we thought a more thorough examination was in order — especially as their hatching time is just around the corner. Jay F. Brenner, Director of WSU’s Tree Fruit Research & Extension Center, gives us some background on this particular family of lepidoptera.
The western tent caterpillar is found throughout the western United States and Canada. There are several species in the western United States, but all have similar life histories, habits and appearances.
The forest tent caterpillar is found throughout North America. While the larvae do trail webbing wherever they go, this webbing does not function as a true tent. However, the webbing may completely cover limbs and foliage. When not feeding, the larvae gather in masses on branches or the tree trunk.
The western tent caterpillar attacks a wide range of hosts including apple, peach, plum, cherry, pear, wild rose, poplar and willow. The forest tent caterpillar prefers maple but will also feed on the foliage of most types of fruit trees.
Egg: The egg is elongated and about 1/25 inch (1 mm) long. Eggs are laid in masses of as many as 400. The masses are covered with a brownish gray material that protects them from the weather.
Larva: The fully grown western tent caterpillar larva is about 2 inches (50 mm) long and covered with fine, soft yellowish brown hairs. The body is pale blue-gray on the sides with a distinctive light stripe down the middle of its back and bluish spots to either side of the mid-line. The fully grown forest tent caterpillar larva can be distinguished from the western tent caterpillar by the row of wedge- or club-shaped cream spots down its back in place of the stripe.
Pupa: The pupa is brown and about 3/4 inch (19 mm) long. It is enclosed in a silken cocoon of loosely woven white silk, which is commonly dusted over with a fine yellowish powder.
Adult: The western tent caterpillar moth is a dull, reddish brown with a pair of parallel oblique whitish bands crossing the front wing. On the forest tent caterpillar the bands are brown.
Tent caterpillars have one generation each year. Tent caterpillars overwinter as eggs, which hatch in spring when new foliage starts to appear. The young larvae move to a crotch and spin a dense web. This web gradually expands as the larvae grow and the feeding area required to sustain the colony increases. Larvae mature in 4 to 6 weeks and by mid-May through June can be seen wandering in search of places to pupate. Moths emerge in June and July, then mate and lay eggs, which hatch the following spring.
Larvae of a single tent caterpillar colony can strip the leaves from a small tree if allowed to develop and are more of a threat in nurseries or newly planted orchards. On larger trees they are only a serious problem if there are several colonies on the same tree. While fruit is not directly attacked, fruit on branches that have had leaves consumed will not develop normally.